For our dedicated freeride wheel, we took our remarkably durable,
flat-spot-resistant Cannibal urethane and poured it in an offset
round-lipped shape, then stone ground the contact patch for smooth
slides right out of the box. The softer red-core 78a hold a line a
little better and tend to leave more distinct urethane lines. Green-core
80a is driftier and slightly more durable.